PHOSPHINE-DIRECTED STEREO-SELECTIVE AND REGIOSELECTIVE NI-CATALYZED REACTIONS OF GRIGNARD-REAGENTS WITH ALLYLIC ETHERS

Studies on the directed regio- and stereoselective M-catalyzed allylic substitution reactions involving methyl- and phenylmagnesium bromides and various acyclic and cyclic allylic ethers are reported. In the pr esence of a properly positioned internal Lewis base, C-C bonds can be formed catalytically and with excellent levels of selectivity. Interna l chelation allows Ni-catalyzed C-C bond forming reactions that are ot herwise non-selective, sluggish, or do not occur at all, to proceed to completion readily, in excellent yields, at ambient temperature and w ith high regio-and stereocontrol. Directed alkene isomerization highli ghts an especially attractive feature of the metal-catalyzed alkylatio n strategy: because the initial product contains a prostereogenic site that remains within reach of the internal Lewis base, it can be subje cted to additional directed stereoselective manipulations. (C) 1998 El sevier Science Ltd. All rights reserved.